Mercury in wet flue gas cleaning

A theoretical model is developed based on thermodynamics, coordination chemistry and electrochemistry. This model leads to an improved understanding of the ligand exchange reactions during the washing process. Calculations of thermodynamic equilibrium by minimizing Gibbs energy complete the investigations with regard to the equilibrium of the mercury complexes and the Henry-behaviour of the volatile species. Proceeding in this way allows both the cause and magnitude of the influencing parameters to be evaluated. The investigations point to the influence of ligand strength and ligand excess in relation to the concentration of bivalent mercury in the washing liquid as major factors on the removal of bivalent mercury. The influence of temperature, redox-potential and pH value is less significant. The importance of the results to wet flue gas cleaning systems is highlighted. Proposals are made for optimizing existing plants and for the design of prospective new plants.